Method for producing monosilane and tetraalkoxysilane

ABSTRACT

The present invention relates to a method for producing monosilane and tetraalkoxysilane comprising subjecting alkoxysilane represented by formula (1) 
       H n Si(OR) 4−n   (1)
 
     wherein R represents alkyl group having 1 to 6 carbon atoms and n represents an integer of from 1 to 3, to disproportionation reaction in a gaseous phase in the presence of an inorganic phosphate or a catalyst having a specific chemical structure based on a heteropolyacid salt structure. In the production method of the present invention, separation from the solvent can be carried out easily, the reaction proceeds quickly and the conversion rate of the starting materials is high.

TECHNICAL FIELD

The present invention relates to a method for producing monosilane andtetraalkoxysilane by disproportionation reaction of alkoxysilane.

BACKGROUND ART

Monosilane is useful as a volatile silicone material having high purity,and has been widely used for producing solar cells, semiconductors,amorphous photosensitive silicone materials and various ceramicmaterials.

Various methods for producing monosilane have been known to date. Amethod using reaction between magnesium silicide and acid or ammoniumbromide, a method by reducing silicon chloride using LiAlH₄, a method byreducing silicon tetrafluoride using CaH₂ and a method bydisproportionation reaction of alkoxysilane have been known.

Trialkoxysilane is generally used as a starting material in thedisproportionation reaction of alkoxysilane, and monosilane andtetraalkoxysilane are produced according to the formula as follows:

4HSi(OR)₃→SiH₄+3Si(OR)₄   [Chem. 1]

Like monosilane, tetraalkoxysilane is a useful chemical substance as apure silicon precursor material for producing various silicon compoundsfor optical fibers, photomasks and IC sealing materials.

Triethoxysilane and trimethoxysilane are used as a starting material inthe above-mentioned disproportionation reaction and tetraethoxysilaneand tetramethoxysilane are produced at the same time as monosilane,respectively, as shown in the following formulae.

4HSi(OMe)₃→SiH₄+3Si(OMe)₄

4HSi(OEt)₃→SiH₄+3Si(OEt)₄   [Chem. 2]

When the above reaction is conducted, metal sodium can be used as acatalyst of the disproportionation reaction. However, the yield is lowin the reaction and therefore the method was not practically useful.

Patent Document 1 (U.S. Pat. No. 4,016,188) discloses a method usingalkali metal alkoxide or alkali metal silicate as a catalyst. However,the reaction in a liquid phase is too slow such that the reaction timeexceeds ten hours, and therefore the method is not suitable forindustrial production.

Patent Document 2 (JP-A-2001-19418) discloses a method for producingmonosilane and tetraalkoxysilane by disproportionation of alkoxysilanerepresented by formula H_(n)Si(OR)_(4−n) wherein n is 1, 2 or 3 and Rrepresents alkyl group or cycloalkyl group, comprising (i) a reactionstep of obtaining monosilane and tetraalkoxysilane by disproportionationof alkoxysilane in a solvent in the presence of a catalyst, (ii) a stepof extracting part of the solvent containing a catalyst andtetraalkoxysilane from the reaction step, and (iii) a step of separatingpart or all of the tetraalkoxysilane by distilling the extracted solventcontaining a catalyst and tetraalkoxysilane.

However, the method also employs disproportionation reaction in asolution and has a problem of difficulties in separation from thesolvent and a problem of insufficient reaction rate.

Patent document 3 (WO 2008/042445 pamphlet) discloses a method forproducing monosilane and tetramethoxysilane by disproportionation oftrimethoxysilane on a potassium fluoride (KF) loaded alumina catalyst.Although this method has no problem with a separation of the catalystand the like from the reaction products, conversion of trimethoxysilaneis not sufficiently high.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: U.S. Pat. No. 4,016,188

Patent Document 2: JP-A-2001-19418

Patent Document 3: WO 2008/042445 pamphlet

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An objective of the present invention is to provide a method to solveproblems as mentioned above that separation from the solvent isdifficult, the reaction is too slow and not suitable for industrialproduction and the conversion of the material is low in a method forproducing monosilane and tetraalkoxysilane by disproportionationreaction of alkoxysilane.

Means to Solve the Problems

As a result of intensive studies to solve the above problems in theconventional art, the present inventors have found that the aboveproblems can be solved by disproportionation reaction of alkoxysilanerepresented by formula (1)

[Chem. 3]

H_(n)Si(OR)_(4−n)  (1)

wherein R represents alkyl group having 1 to 6 carbon atoms and nrepresents an integer of from 1 to 3, in a gaseous phase in the presenceof a catalyst having specific chemical structure.

That is, the present invention relates to the following issues:

-   [1] A method for producing monosilane and tetraalkoxysilane    comprising subjecting alkoxysilane represented by formula (1)

[Chem. 4]

H_(n)Si(OR)_(4−n)  (1)

wherein R represents alkyl group having 1 to 6 carbon atoms and nrepresents an integer of from 1 to 3, to disproportionation reaction ina gaseous phase in the presence of a catalyst, which is characterized byuse of at least one kind of catalysts selected from a group of compoundsrepresented by below formulae (I) to (V):

[Chem. 5]

(M^(I) ₂O)z(MO₂) (P₂O₅)x(H₂O)y  (I)

wherein M represents any of Zr, Ti, Sn or Si; M^(I) represents any ofhydrogen atom, NH₄ or alkali metal; x is 0.5 to 4.5, y is 0.15 to 6.5and z is 0.15 to 3.5;

[Chem. 6]

(MO₂) (P₂O₅)x(H₂O)y  (II)

wherein M represents any of Zr, Ti, Sn or Si; x is 0.5 to 4.5 and y is0.15 to 6.5;

[Chem. 7]

(M^(I) ₂O)z(MO₂) (P₂O₅)x  (III)

wherein M represents any of Zr, Ti, Sn or Si; M^(I) represents any ofhydrogen atom, NH₄ or alkali metal; x is 0.5 to 4.5 and z is 0.15 to3.5);

[Chem. 8]

M^(I) _(m) [M^(II) _(n)M^(III) _(k)O_(j)]  (IV)

wherein M^(I) represents any of hydrogen atom, NH₄ or alkali metal;M^(II) represents P(V) or As (V); M^(III) represents W(VI) or Mo (VI); nis an integer of from 1 to 3; k is any of 6, 12, 18 or 24; j is any of24, 40 or 42 and m is an integer determined by the formula: 2j-5n-6k;

[Chem. 9]

M^(I) _(m)[M^(IV) _(n)M^(III) _(k)O_(j)]  (V)

wherein M^(I) represents any of hydrogen atom, NH₄ or alkali metal;M^(IV) represents any of Si(IV), Ge(IV), Ti(IV) or Ce(IV); M^(III)represents W(VI) or Mo(VI); n is an integer of from 1 to 3; k is any of6, 12, 18 or 24; j is any of 24, 40 or 42 and m is an integer determinedby the formula: 2j-4n-6k.

-   [2] The method for producing monosilane and tetraalkoxysilane as    described in [1] above, using as a catalyst a compound represented    by formula (Ia) in which x is 1 and z is 1 in formula (I);

[Chem. 10]

(M^(I) ₂O) (MO₂) (P₂O₅) (H₂O)y  (Ia)

wherein M and M^(I) have the same meanings as described in [1] above andy is from 0.25 to 4.0.

-   [3] The method for producing monosilane and tetraalkoxysilane as    described in [2] above, wherein M is Zr or Ti.-   [4] The method for producing monosilane and tetraalkoxysilane as    described in [1] above, using as a catalyst a compound represented    by formula (IIa) in which M is Zr and x is 1 in formula (II);

[Chem. 11]

(ZrO₂)(P₂O₅)(H₂O)y  (IIa)

wherein y is 1.0 to 5.0.

-   [5] The method for producing monosilane and tetraalkoxysilane as    described in [4] above, wherein y is 1.3 or 3.-   [6] The method for producing monosilane and tetraalkoxysilane as    described in [1] above, using as a catalyst a compound represented    by formula (IIIa) wherein x is 0.5 and z is 0.5 in formula (III);

[Chem. 12]

(M^(I) ₂O)_(0.5)(MO₂) (P₂O₅)_(0.5)  (IIIa)

wherein M represents Zr or Ti and M^(I) has the same meaning asdescribed in [1] above.

-   [7] The method for producing monosilane and tetraalkoxysilane as    described in [6] above, using a compound represented by a formula in    which M^(I) is K and M is Ti in formula (IIIa);

(K₂O)_(0.5)(TiO₂) (P₂O₅)_(0.5)   [Chem. 13]

-   [8] The method for producing monosilane and tetraalkoxysilane as    described in [1] above, using as a catalyst a compound represented    by formula (IVa) in which M^(II) is P(V) and n is 1 in formula (IV);

[Chem. 14]

M^(I) _(m)[PM^(III) _(k)O_(j)]  (IVa)

wherein M^(I), M^(III), k, j and m have the same meanings as describedin [1] above.

-   [9] The method for producing monosilane and tetraalkoxysilane as    described in [1] above, using as a catalyst a compound represented    by formula (Va) in which M^(IV) is Si(IV) and n is 1 in formula V;

[Chem. 15]

M^(I) _(m)[SiM^(III) _(k)O_(j)]  (Va)

wherein M^(I), M^(III), k, j and m have the same meanings as describedin [1] above.

-   [10] The method for producing monosilane and tetraalkoxysilane as    described in [9] above, using a compound represented by a formula in    which M^(I) is K, M^(III) is W(VI), k is 12, j is 40 and m is 4 in    formula (Va);

K₄[SiW₁₂O₄₀]  [Chem. 16]

EFFECTS OF THE INVENTION

By subjecting alkoxysilane to reaction in a gaseous phase using acatalyst having a specific chemical structure, the method of the presentinvention can solve the problems involved in a method for producingmonosilane and tetraalkoxysilane by disproportionation of alkoxysilanethat separation from a solvent is difficult, the reaction rate is veryslow and the conversion of the starting material is low.

MODE FOR CARRYING OUT THE INVENTION

The method for producing monosilane and tetraalkoxysilane of the presentinvention is to be described in details below.

The present invention relates to a method for producing monosilane andtetraalkoxysilane, characterized in subjecting alkoxysilane representedby formula (1) to disproportionation reaction in gaseous phase in thepresence of a catalyst having a specific chemical structure.

[Chem. 17]

H_(n)Si(OR)_(4−n)  (1)

In the formula, R represents alkyl group having 1 to 6 carbon atoms andn represents an integer of from 1 to 3.

Examples of alkoxysilane represented by formula (1) as a startingmaterial of the disproportionation reaction in the present inventioninclude monoalkoxysilane, dialkoxysilane and trialkoxysilane. Rrepresents alkyl group having 1 to 6 carbon atoms, and preferably alkylgroup having 1 to 2 carbon atoms. Particularly preferred examples ofalkoxysilane include monomethoxysilane, dimethoxysilane,trimethoxysilane, monoethoxysilane, diethoxysilane and triethoxysilane.Among these, trimethoxysilane and triethoxysilane are most preferable.

Disproportionation catalyst for the method of the present invention isan inorganic catalyst having a chemical structure based on phosphate orheteropolyacid salt structure.

The first disproportionation catalyst of alkoxysilane of the presentinvention is selected from a group of inorganic phosphate having thebelow chemical structure;

[Chem. 18]

(M^(I) ₂O)z(MO₂) (P₂O₅)x(H₂O)y,  (I)

In the formula, M represents any of Zr, Ti, Sn or Si; M^(I) representsany of hydrogen atom, NH₄ or alkali metal; x is from 0.5 to 4.5; y isfrom 0.15 to 6.5 and z is from 0.15 to 3.5.

There are several methods for preparing the above-mentioned phosphatecatalyst composition. A general method is to form a sol of metal oxideselected from Zr, Ti, Sn and Si in an aqueos solution at low temperatureby a known appropriate procedure. Examples include a method ofhydrolysis of alkoxide and a method of deflocculation of precipitationof metal oxide (MO₂) selected from Zr, Ti, Sn or Si by phosphoric acidor alkali. The obtained sol can be stabilized with a phosphoric acidsolution and is accumulated by the subsequent heating or alkalitreatment. Further, a conventionally known high-temperature heatingtreatment can be provided to the mixture of the equivalent salt oroxide. Another example is a freezing chemical method includingpreparation of a catalyst core in an aqueous solution, andlow-temperature sublimation and stabilization of the catalyst.

Among the catalysts represented by the above formula (I), preferable arethe compounds represented by formula (Ia) wherein x is 1 and z is 1;

[Chem. 19]

(M^(I) ₂O) (MO₂) (P₂O₅) (H₂O)y  (Ia)

In the formula, M and M¹ have the same meanings as mentioned above, andy is from 0.25 to 4.0, and particularly preferable are the compounds inwhich M is Zr or Ti.

The catalyst of this group represents mixed phosphate of monovalentcation and metal selected from Zr, Ti, Sn or Si. Examples of the saltsinclude K₂Ti (PO₄)₂ (H₂O)_(0.3), i.e. (K₂O) (TiO₂) (P₂O₅) (H₂O)_(0.3).It can be prepared in a form of half-hydrate by ordinarily anealing themixture of TiO₂ and KH₂PO₄ at a molar ratio of 1:2 and 15 mass % ofwater at high temperature. The mixture is to be heated up to 400 ° C.while releasing moisture slowly.

The second disproportionation catalyst of alkoxysilane of the presentinvention is selected from a group of inorganic phosphate having thebelow chemical structure;

[Chem. 20]

(MO₂) (P₂O₅)x(H₂O)y  (II)

In the formula, M represents any of Zr, Ti, Sn or Si; and x is from 0.5to 4.5 and y is from 0.15 to 6.5. Among the catalysts represented by theabove formula (II), preferable are the compounds represented by formula(IIa) wherein M is Zr and x is 1;

[Chem. 21]

(ZrO₂) (P₂O₅) (H₂O)y  (IIa)

In the formula, y is from 1.5 to 5.0. The compound represented byformula (IIa) is known as zirconium phosphate represented asZr(HPO₄)₂·nH₂O. Among these, the compound represented by (ZrO₂)(P₂O₅)(H₂O)_(1.3) wherein y is 1.3 and (ZrO₂) (P₂O₅) (H₂O)₃ wherein y is 3 areparticularly preferable. These compounds can be represented asZr(HPO₄)₂19 0.3H₂O and Zr(HPO₄)₂·2H₂O.

The third disproportionation catalyst of alkoxysilane of the presentinvention is selected from a group of inorganic phosphate having thebelow chemical structure;

[Chem. 22]

(M^(I) ₂O)z(MO₂) (P₂O₅)x  (III)

In the formula, M represents any of Zr, Ti, Sn or Si. M^(I) representsany of hydrogen atom, NH₄ or alkali metal. x is from 0.5 to 4.5 and z isfrom 0.15 to 3.5.

Among the catalysts represented by the above formula (III), preferableare compounds represented by formula (IIIa) wherein x is 0.5 and z is0.5.

[Chem. 23]

(M^(I) ₂O)_(0.5)(MO₂) (P₂O₅)_(0.5)  (IIIa)

In the formula, M represents Zr or Ti. M^(I) has the same meaning as theabove. The compounds represented by formula (IIIa) can be described asM^(I)(MO)PO₄. Among these, particularly preferable is the formula(K₂O)_(0.5)(TiO₂) (P₂O₅)_(0.5) in which M^(I) is K and M is Ti, i.e.K(TiO)PO₄.

The catalyst can be prepared by several appropriate methods. An exampleof the methods for production is as below:

-   -   (a) A colloid solution (TiO₂ precursor from titanium        tetraalkoxide or oxychloride) is prepared.    -   (b) The sol solution is mixed with dilute aqueous solution of        phosphoric acid and potassium carbonate.    -   (c) K(TiO)PO₄ colloid solution obtained by the above mixture is        applied onto a γ-alumina support and subject to heat treatment        at temperature of 500 to 550° C. The formation of K(TiO)PO₄ is        confirmed by analyzing the part coated with the solution.

The fourth disproportionation catalyst of alkoxysilane of the presentinvention is selected from a group of compounds having the belowchemical structure.

[Chem. 24]

M^(I) _(m)[M^(II) _(n)M^(III) _(k)O_(j)]  (IV)

In the formula, M^(I) represents any of hydrogen atom, NH₄ or alkalimetal; M^(II) represents P(V) or As(V); M^(III) represents W(VI) orMo(VI); n is an integer of from 1 to 3; k is 6, 12, 18 or 24; j is 24,40 or 42; and m is an integer determined by the formula: 2j-5n-6k.

The catalyst of the group is an anionic complex compound, i.e. aheteropoly acid having hexavalent ligand around element M^(II) whichforms a complex in the internal coordinate area. The catalyst representsheteropoly acid having a monovalent cation or salt thereof, includespentavalent phosphorus and arsenic as elements forming a complex, andhas a molybdenum salt or tungsten salt as an anionic ligand in theinternal coordinate area.

Among the catalysts represented by the above formula (IV), preferableare the compounds represented by formula (IVa) wherein M^(II) is P(V)and n is 1.

[Chem. 25]

M^(I) _(m)[PM^(III) _(k)O_(j)]  (IVa)

In the formula, M^(I), M^(III), k, j and m have the same meanings asmentioned above.

Examples of catalysts of this kind include K₃[PMo₁₂O₄₀], H₇[PMo₁₂O₄₂],H₃[PMo₁₂O₄₀] and H₇[PW₁₂O₄₂].

The fifth disproportionation catalyst of alkoxysilane of the presentinvention is selected from a group of compounds having the belowchemical structure.

[Chem. 26]

M^(I) _(m)[M^(IV) _(n)M^(III) _(k)O_(j)]  (V)

In the above formula (V), M^(I) represents any of hydrogen atom, NH₄ oralkali metal; M^(IV) represents Si(IV), Ge(IV), Ti(IV) or Ce(IV);M^(III) represents W(VI) or Mo(VI); n is an integer of from 1 to 3; k is6, 12, 18 or 24; j is 24, 40 or 42; and m is an integer determined bythe formula: (2j-4n-6k).

Catalysts of this group also relate to heteropoly acid or salt thereof.These catalysts contain Si(IV), Ge(IV), Ti(IV) or Ce(IV) which arequadrivalent metals as an element forming a complex.

Among the catalysts represented by the above formula (V), preferable arethe compounds represented by formula (Va) wherein M^(IV) is Si(IV) and nis 1.

[Chem. 27]

M^(I) _(m)[SiM^(III) _(k)O_(j)]  (Va)

In the formula, M^(I), M^(III), k, j and m have the same meanings asmentioned above.

Examples of catalyst of this kind include Na₈[TiMo₆O₂₄] andK₄[SiW₁₂O₄₀]. K₄[SiW₁₂O₄₀] is particularly preferable.

Catalyst represented by the above formula (IV) or (V) can be prepared byan appropriate method known as a method for preparation of eachheteropoly acid or salt thereof.

A typical method is reacting molybdenum salt or tungsten salt withphosphoric acid in an acid aqueous solution, followed by drying. Thereaction in the case of molybdenum salt is as below:

H₃PO₄+12Na₂MoO₄+12H₂SO₄→>H₃[PMo₁₂O₄₀]+12Na₂SO₄+12H₂O  [Chem. 28]

Subsequently, the targeted catalyst is obtained by evaporating moisturepartially, impregnating inorganic support with a catalyst solution andsubjecting the support to heating treatment. Corresponding heteropolyacid is prepared by a method selected from the two methods which are:

-   -   (i) treating the heteropoly acid with metal hydroxide or        carbonate slowly, or    -   (ii) neutralizing the surface of the supported heteropoly acid        by cation exchange method.

The catalyst structures of the present invention are used in the solidstate in most cases.

They can be used in either form which is a form of solid granulatedsubstance or a form in which a catalyst is supported on an inertinorganic support made of alumina, titania, silica, carbon or otherkinds.

The other specific examples of preparation methods of catalyst include adeposition of the catalyst of the present invention on a surface of ionexchange resin. An example of ion exchange resin useful for preparing asupported catalyst of the present invention is a cross-linking cationexchange resin without having a phosphoric acid group.

It is effective to use the thus-obtained catalyst in an amount of atleast 0.02 parts by mass to 100 parts by mass of alkoxysilane as astarting material. The catalyst is used in an amount of from 0.02 to 50parts by mass generally, and preferably in an amount of from 0.1 to 20parts by mass.

The disproportionation reaction can be performed either in a batch modeor a continuous flow mode. Alkoxysilane used as a starting material andthe catalyst do not have high chemical reactivity. Therefore, theprocess can be carried out without particular limitations on thematerial of the apparatus.

Accordingly, various types of reactors can be used in the process andtherefore the process can be said to be a catalyst system suitable foran industrial production method.

It is preferable to perform the disproportionation reaction upon heatingand under atmospheric pressure. The preferable temperature variesdepending on alkoxysilane to be used as a starting material and isgenerally in a range of from 100 to 200° C.

The reaction pressure of the disproportionation reaction can be setwithin a range of from 0.2 to 10 atmospheres. Since the reaction is nothighly pressure-dependent, it is preferable to perform the process underatmospheric pressure. However, it is known that monosilane as a reactionproduct is ready to ignite on contact with air. Therefore, to preventthe reaction medium including monosilane from igniting on exposure toair, it is preferable to perform the reaction under inert gas atmospheresuch as nitrogen or argon.

Monosilane generated by the reaction has a boiling point of −111.9° C.and collected in the form of gas after being taken out from the reactor.When the reaction is performed in a batch method, tetraalkoxysilaneremains in the reactor. When a reactor of a flow method is used,tetraalkoxysilane and unreacted trialkoxysilane pass through thereactor, tetraalkoxysilane is condensed and trialkoxysilane is to bereturned to the catalyst reactor. The catalyst used in the presentinvention is insoluble both in starting materials and a reactionproduct, and can be used for a long-term operation period.

EXAMPLES

The invention will be described with reference to Examples below, butthe invention is not limited thereto.

Comparative Example 1

Active potassium fluoride was prepared by slowly evaporating a solventof a solution of potassium fluoride and dried methanol (1:13 to 20 partsby mass) under reduced pressure so as to recrystallize potassiumfluoride and then drying it while raising the temperature.

It is preferable not only to use the methanol for purification havingpurity higher than 99.9% which complies with US Pharmacopeia tests by A.C. S. but also to use dry nitrogen atmosphere. In the process ofevaporating methanol, the temperature is preferably 25 to 35° C.

The subsequent process of drying in vacuum should be performed at leastfor 5 to 6 hours within the temperature range of 75 to 120° C.

The alumina having potassium fluoride supported thereon is prepared asfollows. 30 g of neutral alumina having a particle diameter of 0.3 to1.0 mm and 20 g of potassium fluoride prepared by recrystalization asthe above are mixed with 200 ml deionized water. A solvent is evaporatedat 50 to 60° C. while being lightly deaerated. The remaining product isdried for three hours while being deaerated.

Next, using the product as a catalyst for disproportionation reaction oftrimethoxysilane, the process for preparing monosilane andtetraalkoxysilane was performed as follows. 1.0 g of alumina on whichpotassium fluoride is supported was charged in a reaction tube made ofPyrex (registered trademark) glass provided with an electric furnace andheated to 120° C. The mixture of evaporated trimethoxysilane (flow rate:3.5 ml/min.) and helium (flow rate: 35 ml/min.) was heated to 120° C. ina preheater and next supplied to a reaction tube to thereby performdisproportionation reaction at 120° C. The reaction mixture in the formof gas taken out from the reaction tube was subjected to gaschromatography (GC) analysis for every 20 minutes.

Ten minutes after the reaction had started, the ratio of unreactedtrimethoxysilane, generated monosilane and tetramethoxysilane wassubstantially constant in the reaction product. Dimethoxysilane andmonomethoxysilane were not detected the first one hour after thereaction had started.

The analysis after performing the reaction in a flow reactor system forfive hours showed the following results.

That is, the trimethoxysilane conversion was 63%, the yield ofmonosilane to the supplied trimethoxysilane was 63% (in other words, theyield of monosilane to the converted trimethoxysilane was 100%) and theyield of tetramethoxysilane to the supplied trimethoxysilane was 63% (inother words, the yield of tetramethoxysilane to the convertedtrimethoxysilane was 100%). No by-product was found by the gaschromatography.

Example 1

Hydrated zirconium dioxide sol was treated with 1.0 M/l of H₃PO₄solution at an atom ratio P/Zr as 2.0 and dried at 105° C. until itbecomes to a certain weight. The obtained granular product is sphericalin shape having a diameter of 0.8 to 1.6 mm and the specific surfacearea of 35 m²/g. X-ray test showed that the product is amorphous.According to chemical analysis, this product has chemical structure inwhich x is 1 and y is 3 in the above formula (II). That means, thechemical structure of the obtained product corresponds to the formula:(ZrO₂)(P₂O₅)(H₂O)₃. It can be also described as Zr(HPO₄)₂·2H₂O. Theproduct was filled in a test cell, and preheated at 130° C. for one hourunder helium flow before trimethoxysilane was supplied. Thus-obtainedproduct was used as a catalyst for trimethoxysilane disproportionationreaction, and the catalyst activity was evaluated in a similar manner ascomparative example 1. Table 1 shows the result.

Examples 2 to 9

Catalysts of examples 2 to 9 were prepared in accordance with the belowmethod.

Catalyst of example 2: Catalyst of example 1 was treated with a sodiumchloride solution for ion exchange, and washed and dried.

Catalyst of example 3: Catalyst of example 1 was titrated with apotassium carbonate K₂CO₃ solution, and washed and dried.

Catalyst of example 4: Titanium oxide (TiO₂) was mixed with 15 mass %aqueous solution of potassium dihydrogen phosphate (KH₂PO₄) at a molarratio of TiO₂:KH₂PO₄ as 1:2, and dried with heat until no liquidremains.

Catalyst of example 5: Titanium oxide (TiO₂) was treated with aphosphoric acid (H₃PO₄) solution and a potassium carbonate (K₂CO₃)solution, and the formed K(TiO)PO₄ sol was applied on alumina (γ-Al₂O₃).

Catalyst of example 6: Phosphotungstic acid supported on carbonparticles,

Catalyst of example 7: Sodium phosphomolybdic acid supported on carbonparticles,

Catalyst of example 8: Mixture of ammonium phosphotungstic acid powderand alumina pellets,

Catalyst of example 9: Mixture of potassium silicotungstic acid powderand alumina pellets.

The above-mentioned catalysts were used as a catalyst fortrimethoxysilane disproportionation reaction, and the catalysticactivity was evaluated.

The trimethoxysilane disproportionation reaction and analysis of theproducts thereof was performed in the similar manner as comparativeexample 1. Each catalyst was filled in a test cell and preheated at thetemperature as described in Table 1 for one hour under helium flowbefore trimethoxysilane was supplied. The results are shown in Table 1.

In examples 1 and 2, reaction products during the first 1 to 1.5 hoursshowed the production of 2 to 3% of methanol and equivalent amount ofdimethylsilanol.

After that period, the result showed that the reaction products weremonosilane and tetramethoxysilane only.

As for the experiments of examples 3 to 8, no product other thanmonosilane and tetramethoxysilane was detected by GC analysis.Accordingly, the selectivity of the process was 100% with respect to theconverted trimethoxysilane. No other reaction product such as alcoholand dimer of hexamethoxydisiloxane was found in the reaction mixture.

All the catalysts used are insoluble in the starting materials andreacted products.

No mass decrease of the catalysts was observed during the reaction. Nodecrease in the catalyst activity was observed during the five-hourreaction, either.

The results in Table 1 show that the catalyst efficiency is high in thepresent invention. A flow reactor system can be used for thesereactions, and the method can be easily applied to the production ofmonosilane and tetraalkoxysilane on a continuous industrial scale.Tetraalkoxysilane can be recovered as liquid and monosilane can berecovered as gas. Therefore, separation of the two is easy.

TABLE 1 Pre-heating Conversion of Example Catalyst temp. (° C.)trimethoxysilane (%) 1 Zr(HPO₄)₂•2H₂O═(ZrO₂)(P₂O₅)(H₂O)₃ 130 94 2(Na₂O)_(0.3)•(ZrO₂)(P₂O₅)(H₂O)_(2.7) 130 96 3(K₂O)_(1.2)(ZrO₂)(P₂O₅)(H₂O)_(1.8) 150 90 4K₂Ti(PO₄)₂(H₂O)_(0.3)═(K₂O)(TiO₂)(P₂O₅)(H₂O)_(0.3) 400 87 5K(TiO)PO₄═(K₂O)_(0.5)(TiO₂)(P₂O₅)_(0.5) 500-550 95 6 H₃[PW₁₂O₄₀] 120 937 Na₇ [PMo₁₂O₄₂] 150 84 8 (NH₄)₃[PW₁₂O₄₀] 130 86 9 K₄[SiW₁₂O₄₀] 150 94

Examples 10 to 15

The disproportionation reaction and the analysis of the products wereperformed in the same way as in comparative example 1 using thecatalysts shown in Table 2 and alkoxysilane.

Regarding the selectivity, the mole percent ratio of tetraalkoxysilaneto the total amount of monoalkoxysilane, dialkoxysilane, trialkoxysilaneand tetraalkoxysilane was calculated. Other impurities such as alcoholand siloxane dimer were not detected in the reaction products. Theresults are shown in Table 2.

TABLE 2 Reaction Type of alkoxysilane Conversion (%)/ Example Catalysttemp. (° C.) as a starting material Selectivity (%) 10Zr(HPO₄)₂•0.3H₂O═(ZrO₂)(P₂O₅)(H₂O)_(1.3) 130 Trimethoxysilane  95/100 11H₃[PW₁₂O₄₀] 130 Dimethoxysilane 72/85 12Zr(HPO₄)₂•0.3H₂O═(ZrO₂)(P₂O₅)(H₂O)_(1.3) 120 Methoxysilane 98/74 13Zr(HPO₄)₂•0.3H₂O═(ZrO₂)(P₂O₅)(H₂O)_(1.3) 180 Triethoxysilane  83/100 14H₃[PW₁₂O₄₀] 170 Diethoxysilane 87/89 15 (NH₄)₃[PW₁₂O₄₀] 170 Ethoxysilane94/66

The results in Table 2 show that the catalyst of the present inventionhas high catalyst efficiency.

The conversion can be improved by making the time of contact between thegaseous reaction mixture and the catalyst in the reactor longer.

1. A method for producing monosilane and tetraalkoxysilane comprisingsubjecting alkoxysilane represented by formula (1)[Chem. 1]H_(n)Si(OR)_(4−n)  (1) wherein R represents alkyl group having 1 to 6carbon atoms and n represents an integer of from 1 to 3, todisproportionation reaction in a gaseous phase in the presence of acatalyst, which is characterized by use of at least one kind ofcatalysts selected from a group of compounds represented by belowformulae (I) to (V):[Chem. 2](M^(I) ₂O)z(MO₂) (P₂O₅)x(H₂O)y  (I) wherein M represents any of Zr, Ti,Sn or Si; M^(I) represents any of hydrogen atom, NH₄ or alkali metal; xis 0.5 to 4.5, y is 0.15 to 6.5 and z is 0.15 to 3.5;[Chem. 3](MO₂) (P₂O₅)x(H₂O)y  (II) wherein M represents any of Zr, Ti, Sn or Si;x is 0.5 to 4.5 and y is 0.15 to 6.5;[Chem. 4](M^(I) ₂O)z(MO₂) (P₂O₅)x  (III) wherein M represents any of Zr, Ti, Snor Si; M^(I) represents any of hydrogen atom, NH₄ or alkali metal; x is0.5 to 4.5 and z is 0.15 to 3.5);[Chem. 5]M^(I) _(m) [M^(II) _(n)M^(III) _(k)O_(j)]  (IV) wherein M^(I) representsany of hydrogen atom, NH₄ or alkali metal; M^(II) represents P(V) or As(V); M^(III) represents W(VI) or Mo (VI); n is an integer of from 1 to3; k is any of 6, 12, 18 or 24; j is any of 24, 40 or 42 and m is aninteger determined by the formula: 2j-5n-6k;[Chem. 6]M^(I) _(m)[M^(IV) _(n)M^(III) _(k)O_(j)]  (V) wherein M^(I) representsany of hydrogen atom, NH₄ or alkali metal; M^(IV) represents any ofSi(IV), Ge(IV), Ti(IV) or Ce(IV); M^(III) represents W(VI) or Mo(VI); nis an integer of from 1 to 3; k is any of 6, 12, 18 or 24; j is any of24, 40 or 42 and m is an integer determined by the formula: 2j-4n-6k. 2.The method for producing monosilane and tetraalkoxysilane as describedin claim 1, using as a catalyst a compound represented by formula (Ia)in which x is 1 and z is 1 in formula (I);[Chem. 7](M^(I) ₂O) (MO₂) (P₂O₅) (H₂O)y  (Ia) wherein M and M^(I) have the samemeanings as described in claim 1 and y is from 0.25 to 4.0.
 3. Themethod for producing monosilane and tetraalkoxysilane as described inclaim 2, wherein M is Zr or Ti.
 4. The method for producing monosilaneand tetraalkoxysilane as described in claim 1, using as a catalyst acompound represented by formula (IIa) in which M is Zr and x is 1 informula (II);[Chem. 8](ZrO₂) (P₂O₅) (H₂O)y  (IIa) wherein y is 1.0 to 5.0.
 5. The method forproducing monosilane and tetraalkoxysilane as described in claim 4,wherein y is 1.3 or
 3. 6. The method for producing monosilane andtetraalkoxysilane as described in claim 1, using as a catalyst acompound represented by formula (IIIa) wherein x is 0.5 and z is 0.5 informula (III);[Chem. 9](M^(I) ₂O)_(0.5)(MO₂) (P₂O₅)_(0.5)  (IIIa) wherein M represents Zr or Tiand M^(I) has the same meaning as described in claim
 1. 7. The methodfor producing monosilane and tetraalkoxysilane as described in claim 6,using a compound represented by a formula in which M^(I) is K and M isTi in formula (IIIa);(K₂O)_(0.5)(TiO₂) (P₂O₅)_(0.5)  [Chem. 10]
 8. The method for producingmonosilane and tetraalkoxysilane as described in claim 1, using as acatalyst a compound represented by formula (IVa) in which M^(II) is P(V)and n is 1 in formula (IV);[Chem. 11]M^(I) _(m)[PM^(III) _(k)O_(j)]  (IVa) wherein M^(I), M^(III), k, j and mhave the same meanings as described in claim
 1. 9. The method forproducing monosilane and tetraalkoxysilane as described in claim 1,using as a catalyst a compound represented by formula (Va) in whichM^(IV) is Si (IV) and n is 1 in formula V;[Chem. 12]M^(I) _(m)[SiM^(III) _(k)O_(j)]  (Va) wherein M^(I), M^(III), k, j and mhave the same meanings as described in claim
 1. 10. The method forproducing monosilane and tetraalkoxysilane as described in claim 9,using a compound represented by a formula in which M^(I) is K, M^(III)is W (VI), k is 12, j is 40 and m is 4 in formula (Va);K₄[SiW₁₂O₄₀]  [Chem. 13]